Ten percent of total system cost as a rough guide to the total amount spent on ALL cables: Powercords, interconnects, speaker cables.
This 'amount' is a good compromise between the 'wire is just wire' crowd, and the 'exotic cable are the MAN!' crowd.
I have average $5,000. spent for each main component, and for ALL cabling have very close to 10% spent on cables.
If I add in the cost of my power conditioners, that rises to 15% of total system cost (I do cheat, as the power conditioner is also used for the video stuff, so i allow part of the power conditioner cost for video. If I excluded video, the total of all cable and PC cost would be 18% of system... Rather high I have to say.. but i like my power conditioning!
My take on cables is if you are going to exceed 10% for cables, you would be better off spending that money on basic equipment costs.
I have reiterated this philosopy many times over the years.
A bunch of folks think spending way more on cables is wonderful. Fine, no problem for them.
My advice is for the person who does not know, (like the OP) what sort of budget to make for cables. 10% works great.
Good luck.